Hello @FruTexR
I tried checking for specific numbers so I can give you a better answer, but I couldnāt find that information. When a specific Seige weapon gets upgraded, the effect it does becomes more stronger, and each weapon have different effects. So this means that the key effect each weapon is made for, is improved.
What is the difference between the tiers on each weapon?
I couldnāt find specific numbers, but it upgrades the weapons effect. Fort upgrades revolve around enhancing the areaās defenses, ranging from stronger gates to the ability to deploy more emplacements. Keeping a fort will require as many of these upgrades as possible. For example, each upgrade has 3 Tiers, improving the effectiveness of the defensive structure/weapon. In the case of Gates, each upgrade improves the HP of all gates. Emplacement Point upgrades allow for the placement of more Siege Weapons. Following the same logic, improving Ballista, Explosive Cannon, Repeater Turret, and Fire Dropper to a higher tier will improve their damage. And improving the Horn of Resilience will improve the defensive buff it provides.
Does Ballista applies rend to enemies?
Ballista - has a medium rate of fire, very high damage per shot, and is most effective against structures and large, slower-moving targets, it appears that rend is not mentioned anywhere so this is not confirmed
Do they have more health with higher tier?
For some it does, specifically with Gates but for others it enhances itās key effects.
Do they do more damage?
Upgrading a tier upgrades the effect of the specific weapon, if itās meant for damage, upgrading it increases what it inflicts.
Hope this information helps 